Field attributes and organic geochemical analysis of shales from early to middle Permian Dohol Formation, Peninsular Malaysia: Implications for hydrocarbon generation potential

The early to middle Permian Dohol Formation falls under the Eastern Belt of Peninsular Malaysia. This formation is part of the Palaeozoic rock sequence in East Johor, composed of several metasedimentary, metamorphic, volcanic, and siliciclastic rocks. The Dohol Formation is said to have abundant black shales; however, the previous studies done in the area does not focus on the field attributes and the ability of the shales to generate hydrocarbons. Detailed traditional fieldwork was conducted in East Johor to characterize the shale facies of the formation. Different types of shale facies have been identified and interpreted in this study: (i) dark grey shale facies, (ii) light grey shale facies, (iii) red shale facies, and (iv) dark brown shale facies. XRD analysis was used to evaluate the mineralogy of the rock samples; the results show that the shales are primarily composed of kaolinite, illite, and quartz. The organic geochemical analysis also revealed that the samples collected had low TOC content, with an average TOC value of 0.40 wt%, with type II and type III kerogen predominating. The R_o and Tmax values and plots indicated that the samples are mature, with most already generating oil. The findings of this study suggest that the Dohol Formation has a low potential for generating hydrocarbons in commercial quantities, and also, the rocks are from a deep marine depositional setting.